I can only compare the sound of these two against the Diesel 2x15 that they replaced. To my ears, the sound is the same. Again, to my ears, my sound hasn't materially changed throughout my journey from full valve, through valve/mos:fet to valve/digital. That's been an entirely Mesa powered transition.
That was (for comparisons sake)
Bass 400 - Diesel 2x15
M-Pulse 600 - Diesel 2x15
M-Pulse 600 - Subway 1x15s
TT-800 - Subway 1x15s